Beneteau and all the other Euro production manufacturers use plated brass ball valves. This is absolutely stupid and a long known problem due to the dezincification mentioned by a previous poster. TaKe a look at one ofPaul Stevens articles on this issue.

Grounding and bonding are two entirely different things for different purposes.
You should be immediately suspicious of anyone who uses the term "electrolysis" as this clearly shows they have questionable knowledge of the issue.

ELECTROLYSIS : Chemical changes in a solution or electrolyte due to the passage of electric current.

As you can see from the definition above, electrolysis is what happens to the electrolyte (water), not what happens to any metallic components. This term has come to be applied to virtually all marine corrosion but what we are really talking about are only two different types of electrically induced corrosion ......

1. Galvanic corrosion : Corrosion that occurs at the anode of a galvanic cell.

You may remember high school chemistry class where a battery was created by connecting two dissimilar metals with wire and immersing the whole contraption in salted water thereby activating magnetic fields and starting an electrochemical process causing current to flow. On a boat with bronze, aluminum, galvanized and stainless steel that are connected with bonding wires or simply touching each other and immersed in the lake...... you accomplish the same thing. The more noble metal is the "cathode", the less noble, the "anode". In this process the less noble metal gives up electrons to the more noble thus weakening the metal, otherwise known as "galvanic corrosion".

The "sacrificial" anodes on your shafts, trim tabs etc. are supposed to sacrifice themselves thereby protecting expensive metal parts. This is why it's important to keep your anodes in good condition and never paint them. let's never refer to anodes as "zincs" as anodes come in three basic materials for different water conditions i.e. Aluminum alloy, and magnesium for fresh and brackish water or zinc for salt water. This topic deserves a little more attention on it's own so take a look at Zincs, Aluminum and Magnesium Anodes.

A vessel suffering from galvanic corrosion is usually the source of it's own problem, although two vessel's linked by shore power grounds can create a galvanic cell between two very close boats.

2. Stray Current corrosion : Corrosion that results from an electrical source causing a metal in contact with an electrolyte (water) to become anodic with respect to some other metal in the same electrolyte.

In simple terms a wire touches something it shouldn't, like a faulty bilge pump float or degraded wiring lying in the bilge sending current into the water, causing one metal to give up electrons and corrode. Again any vessel suffering from this type of corrosion is likely the master of it's own disaster but the culprit could also be a neighboring vessel. This type of corrosion can can eat metals at an alarming rate. I know of one 42' motoryacht that lost both shafts, both rudders and both propellers in a space of less than two weeks.

Complicating this picture somewhat is the fact that DC can be super-imposed on your AC wiring through the common ground on board or the ground in the shore power pedestal we all share on the dock. As all vessels in the marina are connected through shorepower grounds there is potential for widespread damage. Aside from concerns of corrosion there is also potential for electrocution if shorepower cords are allowed to lie in the water let alone the fools that leave their shorepower cord plugged in at the dock while they go out for an afternoon cruise.

Recent tests have shown that AC current from shorepower in the water can also cause corrosion to underwater parts although at a much slower rate than DC. This has been a long argued issue by people who know a lot more about this than me. Ground fault protection systems, galvanic isolators, isolation transformers and impressed current systems are some of the various methods attempting to combat corrosion.

Salt water is generally regarded as a more serious breeding ground for marine corrosion as the salt makes the water more conductive however, polluted fresh water can be even more conductive with the right contaminants.
With our aging fleet of pleasure craft it's likely that at some time, less than expert hands have played with your electrical system. If your vessel is suffering from any electrical faults or unusual corrosion consult with an American Boat and Yacht Council Certified marine electrical technician with specific corrosion control training.

Good stuff, I appreciate this feedback. Correction though, Beneteau at least now currently uses Groco Bronze ball valves and fittings. Not the best as I have learned from you and others but not the plated brass valves you referred to. For them to come to an American manufacturer such as Groco is a hard pill for a EU boat builder to swallow, but Beneteau manufactures boats in the US, to date Sail boats but the new Beneteau Swift Trawler 30' will be made here. About everything in my boat is American product (Cruise Air, Raymarine, Jabsco, Groco, or at least sold by American companies. They still need some help on how to make U.S. electrical outlets but otherwise most everything seems to be top shelf. Anyway, back to the valves, I am sure the through-hulls are Groco, with NPS threads, and that the valves are NPT Groco's attached to those threads. I have learned on this forum the flaw in that construction, however Groco says it is sound practice and they make the two parts to go together for through hull applications. We all know that they also make flanged through hull seacocks which are better and more expensive.

You mean the Glastron/Four Winns Trawler? Actually the 30 has some of the most interesting innovations yet and I can't wait to see how it does. Very modern, very practical. This is just an inkling of the synergy they hope to build.

Just to be clear, the thru-hull fitting and ball valve shown in the original post are NOT made by Groco.

Groco does not say that screwing a ball valve onto a thru-hull is good practice. They recognize that it is done and make an effort to make it work. They recommend that only 1/2" of thru-hull thread be exposed below the ball valve which usually requires a very thick backing block to accomplish.

Groco recommends as best practice to use a flanged valve or flanged adapter fastened to a backing block that is secured permanently to the hull.

Attached are Groco's instructions for installing a below the waterline thru-hull and valve.

Great feedback, sorry for the delay in a response this thing called “work” got in the way of TF
I HATE when that happens.

Our hypothesis is that the water in Marina Del Rey was much hotter than the home port of Alameda. Lots of big boats, shallow muddy bottom, warmer water. In the 2 1/2 years prior to this there was no indication of the Galvonic corrosion (thanks Boat Poker) I have yet had an opportunity to pass these by the Beneteau team for their feedback. Also in addition to shaft collar zincs, rudder and the fixed plate we generally in addition have prop zincs which were not in place for this trip.

The boat was built in France and in talking with several people and as several point out this type of thru hull is common in European built boats. This is not the type of Thru Hull I would have spec’d out but then they didn’t ask me for my feedback

As waddenkruiser points out we did use hose clamps to connect the ground wires. Not pretty but hopefully better than nada.

We are hauling the boat and going to have a thorough look at the condition of all of the thru hulls and will make a call from there.

Not related to this conversation but we are also adding three high capacity Jabsco bilge pumps and alarms to the boat as the only bilge pump that exists now is a single Whale Pump in the Engine room with no water alarm. We are putting one in the bottom of the fore cabin, an additional one in the engine room and one in the port area where the GenSet is.

You still need to check the electrical wiring and the marina to see what might be causing this.

Yes Sir, we are.
She is no longer in that marina as we brought her back up the coast to SF in November from where she was berthed this summer in Marina Del Rey for our summer adventures that took us from SF to San Diego.

We have also since replaced the 220/volt shore power cable as the one that came with the boat was a bit "jury rigged" However even with that cable for 2 years there was no such corrosion in SF.

Yes Sir, we are.
She is no longer in that marina as we brought her back up the coast to SF in November from where she was berthed this summer in Marina Del Rey for our summer adventures that took us from SF to San Diego.

We have also since replaced the 220/volt shore power cable as the one that came with the boat was a bit "jury rigged" However even with that cable for 2 years there was no such corrosion in SF.

So either something changed with your boat or it was something at the other marina.

If hose clamps are required to connect bonding wires to a "seacock" it's almost certainly not an approved seacock. True, UL listed, ABYC compliant Sea Valves are required to include a bonding screw, and quality, flanged seacocks, Groco, Apollo etc do include this feature.

If hose clamps are required to connect bonding wires to a "seacock" it's almost certainly not an approved seacock. True, UL listed, ABYC compliant Sea Valves are required to include a bonding screw, and quality, flanged seacocks, Groco, Apollo etc do include this feature.

AC imposed stray current while not a problem for the boat (no anode/cathode to shed material as the current reverses 60/50 times per sec.) it can injure and kill someone in the water. DC imposed stray current can and will cause significant damage to your boat in a surprisingly short amount of time.

Bonding as FF said can be good or not needed depending. Some boats have no bonding (mine) and are just fine. Test with a silver/silver test cell to be sure.

I recommend an electrical survey every few years. I just did one and it cost me $180 bucks and found another boat nearby with 6.8 Amps worth of leakage into the water due to a ground and neutral connected at a GFI, remember the grounds on a boat are common and should never be connected to the AC neutral.

DC wire laying in bilge water connected to battery is a very big problem looking for a wallet to happen in.

The question of whether to bond various pieces of metal gear and underwater metals in a circuit or leave them isolated is a subject that's sure to generate heated debate. If the argument could be made for one approach or the other without regard to other related grounding issues, then isolation would surely win out. However, other grounding considerations-including electrocution prevention, the mitigation of damage from lightning strikes, and the need to provide a safe path to ground for short circuits in the AC and DC electrical systems-argue in favor of an overall grounding system. Moreover, if done properly, this system helps to minimize stray current corrosion that can affect any node on the circuit.

To make an already complex topic simpler, let's limit the scope to fiberglass boats. The bonding of various metals, such as the stainless steel of rudder stocks, the bronze of seacocks and through-hull fittings, the Aquamet alloy of propeller shafts, and the aluminum of tanks and spars, may seem like an invitation for corrosion. Every effort typically is made to keep dissimilar metals apart, especially those that are far apart from each other on the galvanic scale, such as aluminum and copper alloys.

The key difference with a comprehensive bonding system is that all of these dissimilar metals are part of a circuit that also includes a sacrificial anode, typically made of zinc. Because zinc is especially galvanically ignoble, when it's connected to the DC bonding system, it affords galvanic protection to all other metals above it on the galvanic scale.

Not bonding underwater metals does not eliminate the potential for in water AC current flow, and electrocution, the engine will by default be part of the DC negative system, and the AC safety ground must, for electrocution prevention, be common with it, which gives stray AC leakage current a path to the water. Ideally, an AC fault to a bonded object will cause the source circuit breaker to trip, rendering the fault safe. To make this system safer, ELCI shore power circuit breakers (essentially a GFI for the whole boat, albeit with a higher trip threshold) are now commonly installed on new and refit vessels.

Finally, linking the DC bonding system with the AC safety ground (and the lightning-grounding if present) systems means that most metal masses on board are part of the grounding system, offering both electrocution protection as well as corrosion mitigation. And to protect all the elements of this boat-wide circuit, diligent attention should be paid to the sacrificial zincs that will prevent galvanic corrosion. Frequent inspection and replacement of the zincs when required is a small price to pay in exchange for protection against potentially harmful or life-threatening electrocution scenarios or short circuits from any of the electrical sources aboard boat.

In this case, corrosion of an alloy that contains high levels of zinc may have been staved off for some time by sacrificial anodes as long as they and the bonding system were maintained. The threshold for resistance in the bonding system, between zinc anodes and the protected metal, is very low indeed, it cannot exceed one ohm. Therefore, a little corrosion or a loose or poor connection (using a hose clamp for instance) can easily create enough resistance to block protection otherwise provided by a zinc anode.

For the record, Electric Shock Drowning (ESD) is almost unheard of in saltwater. It happens almost exclusively in freshwater. I have been diving in Bay Area saltwater marinas for 21 years and in that time well over 1,000,000 in-water hull cleaning events have taken place here. To my certain knowledge, no hull cleaner has been injured or killed here due to ESD. That's a pretty good indication that electrical problems (while not to be ignored) do not present a signifcant danger in saltwater, IMHO.

From the BoatUS web site. Maybe not the most technically correct explanaition, but will give you the general idea:

Why fresh water and not salt? Salt-water is anywhere from 50 to 1,000 times more conductive than fresh water. The conductivity of the human body when wet lies between the two, but is much closer to saltwater than fresh. In saltwater, the human body only slows electricity down, so most of it will go around a swimmer on its way back to ground unless the swimmer grabs hold of something — like a propeller or a swim ladder — that's electrified. In fresh water, the current gets "stuck" trying to return to its source and generates voltage gradients that will take a shortcut through the human body. A voltage gradient of just 2 volts AC per foot in fresh water can deliver sufficient current to kill a swimmer who bridges it.

Here is an article on this topic: http://michel-christen.com/2T-H.pdf
It explains in very good detail what the problem is right down to metal composition. I like (sarcasm) that in the EU they specify an underwater thru-hull is to withstand at least five years of use without deterioration that compromises its condition. Not a very high bar to jump...

For the record, Electric Shock Drowning (ESD) is almost unheard of in saltwater. It happens almost exclusively in freshwater.

Correct, ESD is a fresh water issue. I had the great good fortune to take the ABYC Corrosion Analysis course taught by Kevin Ritz. Kevin is the "discoverer" of ESD and his story of losing his 8yr. old son, Lucas to the phenomena is heart breaking. Take the time to watch Kevins' youtube video on this issue.

This has been an interesting thread. Several posters identified stray current corrosion as a possible cause (probable in my view). I didn't see any discussion of causes and remedies. There are two:

One is internal. The most typical is a bilge pump wired backwards or a bare terminal lying in bilge water. That will supply DC voltage to the underwater metals and eat them away quickly whether they are really bronze or just crappy brass. Note the picture of the folding prop above.

The other is external. An adjacent boat has a similar DC to ground problem and that DC voltage comes over to your boat on the shore power ground. It will do the same thing to your boat. A good galvanic isolator will stop most ground leakage. An isolation transformer is even better. Or just keep your shore power unplugged.

One is internal. The most typical is a bilge pump wired backwards or a bare terminal lying in bilge water. That will supply DC voltage to the underwater metals and eat them away quickly whether they are really bronze or just crappy brass.

Never seen a true bronze seacock damaged by galvanic or stray current corrosion.

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